1. Field of the Invention
The present invention relates to a portable electric drill type boring apparatus for boring webs of steel sections such as rails, H sections, I sections and channels.
2. Description of the Related Art
FIG. 8 illustarates a boring apparatus 101 according to a first prior art. This apparatus 101 is a portable electric drill having a magnetic fixing device 100. Procedures of drilling a web 103 of an H section 102 using this boring apparatus 101 will be described referring to FIG. 8.
First, the H section 102 is placed such that the web 103 thereof may be substantially horizontal, and the fixing device 100 is disposed at a predetermined position on the surface of the web 103. The fixing device 100 is fixed on the web 103 by the magnetic force of a magnet. Next, the boring apparatus 101 is descended to drill downward the web 103 at the predetermined position. Drilling of a web of a channel can be performed in the same manner as in the drilling of the H section.
A special section boring apparatus is also known as a second prior art. This boring apparatus drills both flanges 104 and a web 103 using separate drills respectively.
Further, Japanese Unexamined Patent Publication No. Hei 7-9222 descloses a boring apparatus as a third prior art. This boring apparatus described therein has a pair of clamping plates for clamping a pair of side walls of a channel and a drill which is disposed to be movable toward a web present between the thus clamped side walls of the channel. Accordingly, the web can be drilled by operating the drill with the channel being clamped by the clamping plates.
However, according to the first prior art, a section must be placed such that the face to be drilled or the web thereof may assume a horizontal posture and then the fixing device 100 is mounted on the horizontal face, because the boring apparatus 101 is merely magnetically fixed on the web 103, and if the web 103 is not maintained horizontally, the apparatus 101 readily slips out of position.
However, when a heavy section is to be drilled, the section must be handled by a crane so as to allow the face to be drilled thereof to assume a horizontal posture, and in the case of a light section, it must be handled manually by workers, requiring very intricate procedures.
Further, this boring apparatus 101 involves a problem that positioning of the drill at a predetermined point requires intricate procedures since it employs a large and heavy magnet, and thus the apparatus has poor drilling efficiency.
Meanwhile, the special boring apparatus according to the second prior art is generally big and heavy and is a stationary equipment, so that a section must be carried to the apparatus. The section is placed once on a work-table of the apparatus and then set at a drilling position. Accordingly, it takes time and labor to carry sections to the special boring apparatus and also to load and unload the section to and from the work-table.
In the third prior art, a section such as a channel and an H section is clamped by clamping plates before it is subjected to drilling. Accordingly, the section placed on the floor cannot be clamped as such, so that webs of sections placed on the floor cannot be drilled, disadvantageously.
It is a primary objective of the present invention to provide a boring apparatus which enables an operator to bore a web of a section with a lower flange thereof being placed on the floor.